This invention relates generally to rotary wobble plate compressors and more particularly to an improved wobble plate construction wherein the wobble plate is pivoted from a point radially spaced or offset from the axis of the drive shaft so that the no-stroke position, i.e. that position which results in negligible piston movement, corresponds to the top-dead-center position of the pistons.
The advantages of wobble plate type compressors are well recognized in the art. Such compressors (or fluid motors) utilize a plate, the position of which is movable out of a plane normal to the direction of piston travel to permit varying of the stroke and thereby the displacement or capacity of such units. Essentially, such compressors may be considered rotary devices in that a substantial portion of the mass is undergoing a rotary motion, thereby contributing to the smoothness and quietness of operation. On the other hand, the pistons reciprocate and thereby have the advantage of reciprocating piston devices with their convenient adaption for capacity control and efficient sealing. One main difference between the wobble plate type compressor and the conventional reciprocating compressor is that the pistons travel in the same direction as the axis of the rotating drive element, as distinguished from the radially reciprocating motion of pistons in a conventional reciprocating piston device. As is well known in the art, with three or more uniformly spaced, axially reciprocating piston masses, the resulting unbalance is a rotating couple. This couple can be balanced by suitably disposed masses on the rotating shaft, and is usually accomplished in devices of this type by properly sizing the inclined rotating element. These features are responsible for a much smoother, more vibrationless and quieter apparatus, while combining the efficiency of the reciprocating pistons as a gas compressing element.
Heretofore, most wobble plates have been constructed so that they pivot around a point lying along the axis of the drive shaft. While this is satisfactory for hydraulic pumps or motors, it creates a problem with respect to compressing a fluid such as conventional halocarbon refrigerants. In the fully unloaded or no-stroke position, the pistons are disposed approximately half way between their top-dead-center and bottom-dead-center positions. With this type of mechanism, when reducing the stroke from the full stroke condition, the relative clearance volume increases very rapidly with a decrease in stroke. At high pressure ratios, this drastically reduces the pumping capability of the compressor and it will cease to deliver any flow at all long before the zero stroke position is reached.
In the present invention, the wobble plate is adapted to be pivoted from a point which will result in minimal clearance volume at zero capacity and throughout the entire capacity range. Additional features of the invention include means for anchoring the wobble plate against rotation with a universal joint, a means of partially balancing the forces on the pistons and wobble plate to reduce the stress and wear on the moving parts, and an improved capacity control which greatly reduces the losses of this compressor at partial load compared to all other known means of capacity control.